In the field of the lighting equipment design of motor vehicles, a special position is occupied by light guides whose elongated shape makes them suitable to create light lines, e.g. to emit a position, brake, fog, indicator or day light. At present, light guides often fulfill signal light functions subject to higher requirements for the luminous flux, as e.g. the daily light in headlights and the rear brake and direction indication lights in the rear lamps. Semiconductor LEDs (light emitting diodes) are most frequently used to generate light, being positioned at the front of the light guide or installed in a recess in the entry part of light guides. Light guides of thin dimensions do not completely bind light into the light guide and a part of the light rays is lost. For this purpose, collimators are used, which help to bind light to the light guide, which increases the efficiency of the optical system. In some cases, collimators are designed as a separate part.
A number of optical systems are known from the prior art that are adapted to bind light to the light guide and to guide light in the light guide in such a way as to ensure the required light characteristic of the output light trace. E.g. the documents CZ20140711, US20080304277, U.S. Pat. Nos. 6,937,791, 7,215,863 and US2004213001 disclose designs where a collimator is an integral part of the light guide. Generally, collimators with a diameter of 7-15 mm can be advantageously used for effective binding of light, ensuring high efficiency of the system. However, if a collimator with bigger dimensions is used at the input, a thin light emitting output surface cannot be easily provided at the output unless the light guide gets narrower in the direction from the light source. But if the light rays are reflected in various ways inside the light guide body, they may exit under any angle from the output surface, which reduces efficiency with respect to the output characteristic required by regulations. So to increase efficiency of an optical system it is advantageous to get the output light beam directed under a certain angle from the optical axis. The effective angle is defined by the light function and its required output characteristic. Depending on the type of the light function, the horizontal diffusion of the output light should preferably be from 5° to 25°, the vertical diffusion from 5° to 10°. However, variability of the mechanical design of the light device is very often limited, which affects the emission characteristics of the resulting light trace or requires adaptation of the mechanical design of the light device or even redesigning of the entire light guide.
The objective of the invention is to eliminate the shortcomings of the prior art, especially to increase efficiency of the optical system by efficiently binding the light rays of the LED light source to the light guide and by improving the routing and guiding of light propagating through the light guide. Another objective is to ensure diffusion of the output light under the angle of 5° to 25° (or 5° to 10°, respectively), the diffusion of the output light being ensured through a small/narrow output surface to achieve the designer requirements. At the same time, a homogeneous appearance of various shapes of the output light trace must be guaranteed, the light being only emitted to the required area based on the required characteristic of the signal function. The shape of the light guide must be adaptable to the mechanical design of the light device and the required characteristic of the light trace while at the same time, it must have a simple design and low production costs.